This invention relates to electrostatic spraying devices, and, more particularly, to a low voltage electrostatic spraying device in which a stream of electrostatically charged pesticide is dispersed in a wide spray pattern upon the objects to be coated, and electrical hazards of isolating the material supply are reduced.
Electrostatic coating is a process in which a stream of coating material is atomized into finely divided particles which are electrostatically charged. The charged particles are then directed at a surface to be coated which is held at a different electrical potential than the particles. Due to the electrostatic attraction and the proximity of the charged particles to the surface to be coated, electrostatic forces move the particles onto the surface where they are deposited to form a coating or layer.
Many electrostatic coating devices employ high voltages, e.g., 50 kilovolts or more, to create a corona discharge through which the particles pass to become electrostatically charged. One problem with employing high voltages in the application of electrostatic charges to waterborne pesticides for deposition onto trees or other crops, is that waterborne pesticides are highly conductive and the charge applied thereto is transferred back through the pesticide stream to its holding tank. The tank must therefore be electrically isolated from ground. When isolated, the tank becomes charged with the same high voltage as the electrical field, and must be electrically insulated and isolated from the persons spraying the pesticide to avoid serious electrical hazards. Special insulation and mounting of the holding tank of a pesticide sprayer adds substantially to its costs, and therefore the use of corona electrostatic charging of waterborne pesticides has been traditionally cost prohibitive and dangerous.
An electrostatic spraying device for agricultural applications which employs low voltage to inductively charge a stream of waterborne pesticides or similar treatment chemicals is shown, for example, in U.S. Pat. No. 4,004,733 to Law. Electrostatic spray nozzles of this general type comprise a nozzle body formed with a fluid passageway in which a stream of waterborne pesticide is atomized into finely divided droplets or particles. An electrode is mounted in the nozzle body, in axial alignment with the fluid passageway, which is operable to electrostatically charge the particles forming the atomized stream before they exit the nozzle body. The electrostatic charge is applied to the fluid stream at the point of atomization by induction using a voltage on the order of 2 kilovolts, as opposed to ionized field systems which typically employ voltages of 50 kilovolts to 100 kilovolts or higher. The charged particles which are entrained in the stream of air are then expelled through the fluid passageway in the nozzle body, which propels the charged particles onto the trees, grapevines or row crops to be coated.
One limitation of spray devices such as disclosed in U.S. Pat. No. 4,004,733 to Law, is that it produces a narrow spray pattern. Another limitation of electrostatic spray devices of the type described in the Law patent involves the problem of grounding the electrode to the point at which the dielectric nozzle body is connected to ground potential. Charged particles emitted from the discharge orifice accumulate on the exterior surface of the nozzle body near the discharge orifice, and readily migrate along the nozzle body eventually reaching its connection to ground. Grounding of the electrode via the thin film of particles formed along the nozzle body and emitted from the discharge orifice reduces the charging efficiency of the electrode and limits the effectiveness of the spray device in completely coating the target trees or other crops. Yet another limitation of the prior art devices is that they do not comprise multiple component assemblies wherein the key components can be easily disassembled and reassembled for maintenance, repair and replacement of worn or defective parts.